What Does the Infrared Have to Do With Space?

Look at the difference between visible and infrared light! This image dramatically shows the difference of the visible and infrared sky. On the left is a visible image of the constellation of Orion. On the right is an IR image taken by IRAS (IR Astronomical Satellite, the predecessor to SIRTF) illustrating the dust (only around a 100 K or -173 Celcius) present in the Orion Giant Molecular Cloud. SIRTF will Study the Old, the Cold, and the Dusty Many areas of space are filled with vast, dense clouds of gas and dust which block our view. Infrared light, however can penetrate these clouds, allowing us to peer into regions of star formation, the centers of galaxies, and into newly forming planetary systems. Infrared also brings us information about the cooler objects in space, such as smaller stars which are too dim to be detected by their visible light, extrasolar planets, and giant molecular clouds. Also, many molecules in space, including organic molecules, have their unique signatures in the infrared. There are many different kinds of things to look at in the Universe. There are stars, planets, asteroids, comets, galaxies, black holes, and huge dust clouds. These objects all emit different kinds of light because of their different temperatures. Most stars, like our Sun, are really hot. They emit mainly visible light, and that's why we can see them. Cooler objects, like planets and asteroids, emit mainly infrared light. We can't see this with our eyes, but the new SIRTF observatory can see infrared light (the reason that we can see the planets in our solar system is that they reflect the visible light of our Sun, but we still can't see their infrared light with our eyes). SIRTF can look for newly born planetary systems around other stars in our Milky Way Galaxy by looking for the infrared light they emit.

What is Infrared Light? Infrared light is a form of electromagnetic radiation, one that is invisible to our eyes. Infrared light is what we commonly think of as “heat” radiation. Heat is the kinetic energy stored in the motion of atoms and molecules. Infrared light is emitted by anything in the universe with a temperature (above absolute zero). Objects below 1,000 degrees C radiate mostly in the infrared.

Infrared and Temperature Things can look quite different when you look at them in a different light. In the IR image the progression from hot to cooler temperatures is represented by white to yellow to orange to red to magenta to blue to purple to black. People emit IR light whereas the visible light coming from people is all reflected from other light sources. Dr. Michelle Thaller (Senior Scientist, California Institute of Technology) seen with an infrared camera (after playing with an ice cube). Things can look quite different in infrared light.

Properties of Infrared Light Infrared light can pass through many things that block visible light, like smoke and dust (and most plastics). Michelle Inside of Black Plastic Bag Fireman Inside of Smoke-filled Room

Properties of Infrared Light Infrared Light is also blocked by things that let visible light through (like our atmosphere!) A Piece of Glass Completely Blocks Infrared Light

Because of its relatively long wavelength, Infrared Light can travel more readily through Interstellar Dust (similar in size to smoke) than visible light. Dust particles are around 0.5 microns in size which is around the wavelength of visible light. As you move into the infrared beyond 1 micron, the photons interact less and less with these small dust particles. The dust, however, can emit its own IR radiation based on its temperature.

What a difference Temperature Makes (Blackbody Radiation) www.usd.edu/esci/figures/ 158301.JPG To explore how many objects emit Electromagnetic Radiation, play with the interactive on blackbody radiation. The human body behaves very much like a blackbody radiator in the IR part of the spectrum. There are two important aspects of blackbody radiation. When objects get hotter, they put out more radiation at all wavelengths. In fact the amount of energy put out by a blackbody is related to the fourth power of temperature. As an example an object which doubles in temperature will put out 16x more energy. As the Temperature increases the peak of the blackbody radiation moves to shorter wavelengths. That is why hotter objects appear bluer in color and cooler objects appear redder in color. Not all objects are good blackbodies. The aluminum hotplate is an excellent example as it does a poor job of converting its heat into IR radiation. On the flip side, poor blackbodies are good reflectors. Note this with the hotplate.

Infrared Astronomy Explores: Objects in space that are too cool to radiate visible light Planets, interstellar dust clouds, Brown Dwarfs, proto-planetary disks Objects and processes that are obscured by dust Star and planet formation, active galactic nuclei (black holes) The Very Distant Universe Radiation from the early universe has been red-shifted into the infrared Young galaxies appear to be shrouded in dust Interesting Chemistry Spectral lines of water, CO2, organic molecules in infrared region

The Heritage of Infrared Astronomy Infrared discovered in 1800 by William Herschel First infrared telescopes built in 1960’s. Kuiper Airborne Observatory in 1970’s. IRAS (Infrared Astronomical Satellite) in 1983. ISO (Infrared Space Observatory) flown by ESA in 1995. SIRTF (Space Infrared Telescope Facility) launched in 2003.

Failed Stars of the Universe BROWN DWARFS Failed Stars of the Universe http://astron.berkeley.edu/~basri/bdwarfs/sciam1.jpg Brown Dwarfs are good example of cool (less than 1000 K) objects that are best studied in the IR.

The mass of a brown dwarf is no more than eight percent of the Sun’s mass, and many are not much bigger than Jupiter. http://chandra.harvard.edu/graphics/resources/illustrations/twa5b_dwarf_ill_300dpi.jpg The approximate size of a brown dwarf (center) compared to Jupiter left) and the Sun (right). Although brown dwarfs are similar in size to Jupiter, they are much more dense and produce their own light whereas Jupiter shines with reflected light from the Sun.(CXC/K.Kowal)

Infrared Spectra of a Red Dwarf and a Brown Dwarf The major difference in the two is the high level of methane found only in brown dwarfs. http://www2.keck.hawaii.edu/news/browndwarf/spectra.jpg Molecules display strong feature in the IR part of the spectrum.

Extrasolar Planet and Planetary Disk Detection Planets and Planetary Disks are also good examples of cool objects best detected in the IR. In addition the light from the parent star is not as overwhelming in the IR (look at the blackbody curves for different temperatures).

Near Infrared image of Beta Pictoris This is an example of a warm disk of material around a star where planets may be born. This is Beta Pictoris, a star with a disk about it. Places like these will be where scientists will be looking for planets being born. SIRTF will be sensitive to the detection of warm dust that exits in the disks surrounding newly formed stars. Observations in the IR are also less swamped by the light of the star. Near Infrared image of Beta Pictoris

These warm dust disks around stars give clues to the presence of planets

Young stars, mostly unseen, are hidden in these clouds. http://hubblesite.org/newscenter/archive/2000/19/image/c Oscillate between this and the following image to see how well IR penetrates the gas and dust. Visible Light Orion Nebula

What a difference the infrared view makes! http://hubblesite.org/newscenter/archive/2000/19/image/b Infrared view Orion Nebula

Active Galactic Nuclei (Giant Black Holes) What powers the most luminous galaxies in the universe? Perhaps giant black holes fed by turbulent galaxy mergers. Whatever it is lies hidden behind dust.

And Closer to Home… Note how the infrared view is much less obscured by dust. The Center of the Milky Way in visible (left) and infrared (right) shows signs of having a similar massive black hole.

Seeing to the end of the Universe The farthest objects in the universe are heavily red-shifted, in some cases completely out of the visible range. Infrared can probe deeper, exploring the first proto-galaxies as much as 14 billion light years away.

Space Infrared Telescope Facility http://sirtf.caltech.edu/Media/mediaimages/artist_concepts.shtml SIRTF launched on Sunday, August 24, 2003 at 11:35:39 p.m. MDT

Explain how the design of the SIRTF telescope is consistent with what we know about IR radiation. Consisting of a 0.85-meter telescope and three cryogenically-cooled science instruments, SIRTF (Built primarily at Ball Aerospace, Boulder CO) will be the largest infrared telescope ever launched into space. Its highly sensitive instruments will give us a unique view of the Universe and allow us to peer into regions of space which are hidden from optical telescopes. Because infrared is primarily heat radiation, the telescope must be cooled to near absolute zero (-459 degrees Fahrenheit or -273 degrees Celsius) so that it can observe infrared signals from space without interference from the telescope's own heat. Also, the telescope must be protected from the heat of the Sun and the infrared radiation put out by the Earth. To do this, SIRTF will carry a solar shield and will be launched into an Earth-trailing solar orbit. This unique orbit will carry SIRTF far enough away from the Earth to allow the telescope to cool rapidy without having to carry large amounts of cryogen (coolant). This innovative approach has significantly reduced the cost of the mission. Note that one side of the spacecraft is black and the other is silver. The black side emits

Which waves of light cannot be observed from Earth? The Earth's atmosphere lets visible light pass through easily, allowing us to see the Sun during the day and distant stars at night. However, the water vapor in the atmosphere absorbs infrared light from space, and so most infrared light from astronomical objects is blocked by the atmosphere. {Only a very small portion of infrared light reaches us on high mountaintops located in dry environments.} To see most of the infrared light from stars, galaxies and other astronomical objects, we must place a telescope above the atmosphere - typically in space.